1. Technical Field
Embodiments of the present disclosure are directed to a laser crystallizing apparatus, and more particularly, to a laser crystallizing apparatus that crystallizes an amorphous silicon thin film into a polycrystalline silicon thin film by using an excimer laser.
2. Discussion of the Related Art
Methods of preparing a polycrystalline silicon thin film transistor at a low temperature include a solid phase crystallization (SPC) method, a metal induced crystallization (MIC) method, a metal induced lateral crystallization (MILC) method, an excimer laser annealing (ELA) method, etc. In particular, in a process of manufacturing an organic light emitting device (OLED) or a liquid crystal display (LCD), the ELA method of crystallization using a high energy laser beam is used.
An ELA method includes irradiating a laser beam to amorphous silicon to phase-change the amorphous silicon into polycrystalline silicon, and using a cumulative shot process of 20 times or more to crystallize a part of the silicon. When using a 308 nm wavelength UV excimer laser, the UV light is fully absorbed in a wavelength range of about 300 nm to about 400 nm, but because UV light also has a reflectance of about 40% or more, the reflected UV light is not used for crystallization and lost. Because the reflectance of polycrystalline silicon is about 50% or more, in spite of the cumulative shots, the loss thereof is large.
A laser beam incident to a beam splitting polarization module, which is currently used with mass-produced equipment, has a random polarization, and the polarization module has a plurality of lenses and mirrors. The laser beam is converted from a quadrangular beam into a linear beam in the polarization module. When a randomly polarized laser beam is used for grain alignment, a multiple beam of 15 shots or more is required.